Stellan looks at a lit candle through a concave lens held at arm's length. He sees a small, right-way-up candle. He walks closer, then farther: the little candle grows and shrinks slightly, but it never flips and never lands on anything.
The convex lens needed two profiles, one per object position. The concave lens needs only one, because its construction always ends the same way.
Put an object at ANY distance from a concave lens.
The construction always ends the same way: the beam's refracted rays spread, and the image sits where the dashed trace-back crosses the center ray, on the object's side, between the lens and the near focal dot.
Virtual: the rays never actually meet, so no screen or card ever catches the picture.
Upright: the crossing sits on the same side of the principal axis as the object's tip, so nothing flips.
Reduced: the crossing sits closer to the lens than the object and lower than its tip, so the seen picture is smaller than the thing.
Move the object nearer or farther and the little image shifts and changes size a little, but its three words never change.
Stellan's candle keeps its profile at every distance: small, right-way-up, caught by nothing.
With this profile stated, all six element-and-position profiles are now known, and the table below collects them.
You look INTO a mirror, because the light comes back to you, and THROUGH a lens, because the light comes on to you.
Romilly looks at a streetlight through a concave lens, first from across the street, then from close up. Describe what she sees each time.
The concave lens has one always-profile: virtual, upright, reduced.
From across the street: a small, right-way-up streetlight, seen through the glass.
From close up: still a right-way-up, smaller-than-life streetlight, just shifted and resized a little.
Both times she sees a reduced, upright, virtual image; only its size and position shift slightly.
Quill wants to project the candle's picture onto the wall using only the concave lens. What happens when he tries?
Projecting needs a real image: rays that actually meet at the wall.
A concave lens spreads the rays; only the dashed trace-backs meet, on the candle's side.
So nothing lands on the wall, at any lens position.
The wall stays blank: a concave lens alone never projects an image.
A keychain hangs some distance from a concave lens. Describe the image the lens forms.
Stellan slides the candle from 20 cm out to 80 cm from a concave lens. What happens to the image's three-word profile?
Quill says: 'A concave lens on its own never forms an image you can catch on a screen.' Is Quill correct?
A student looks at a parked bus through a concave lens. Which description of what she sees is correct?
Looking THROUGH which element shows a smaller, right-way-up picture at every object distance?
For which object positions does the concave lens's virtual, upright, reduced profile hold?